<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style type="text/css">
        *{
            margin: 0;
            padding: 0;
        }
        #box{
            width: 360px;
            height: 70px;
            padding-top: 360px;
            margin: 200px auto;
            border: 1px solid #ccc;
            background: url(images/01big.jpg) no-repeat top center;
            overflow: hidden;
        }
        ul{
            overflow: hidden;
            list-style: none;
            border: 1px solid #ccc;
        }
        li{
            float: left;
        }
    </style>
    <script>
        window.onload = function(){
            var box = document.getElementById("box");
            function fn(liid,bg){
                var obj = document.getElementById(liid);
                obj.onmouseover = function(){
                    box.style.backgroundImage = bg;
                }
            }    
            fn("li01","url(images/01big.jpg)"); 
            fn("li02","url(images/02big.jpg)"); 
            fn("li03","url(images/03big.jpg)"); 
            fn("li04","url(images/04big.jpg)"); 
            fn("li05","url(images/05big.jpg)"); 
        }
    </script>
</head>
<body>
    <div id="box">
        <ul>
            <li id="li01"><img src="images/01.jpg" alt=""></li>
            <li id="li02"><img src="images/02.jpg" alt=""></li>
            <li id="li03"><img src="images/03.jpg" alt=""></li>
            <li id="li04"><img src="images/04.jpg" alt=""></li>
            <li id="li05"><img src="images/05.jpg" alt=""></li>
        </ul>
    </div>
</body>
</html>